Teacher added to class: The average age of 24 students is 10 years. When the teacher is included, the average increases by 1 year. Determine the age of the teacher.

Introduction / Context:
Adding one data point that raises the average lets us compute that data point by comparing totals before and after inclusion.

Given Data / Assumptions:

• Students = 24, student average = 10 years
• With teacher, count = 25, new average = 11 years

Concept / Approach:
Total = average * count. Teacher age = new total - old total.

Step-by-Step Solution:

Verification / Alternative check:
Check average with teacher: (240 + 35)/25 = 275/25 = 11. Correct.

Why Other Options Are Wrong:

• 25 or 30 years: Insufficient to raise the average by 1.
• 40 years: Would increase the average more than required for these counts.

Common Pitfalls:
Mistaking the direction of change, or forgetting that adding an older person increases the total appropriately.

Final Answer: